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#31
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Double Release Failure
On Sep 10, 8:27*am, Frank Whiteley wrote:
On Sep 10, 2:37*am, (Alan) wrote: In article Jim Beckman writes: At 14:13 08 September 2009, FBCompton wrote: Important Timing Aspect: *The glider (in low tow) must not touch down much before the towplane -- this can be a hazardous aspect -- touching down well before the towplane and stalling it. *The glider wings are still carrying the weight of the glider while it is flying. *Once the glider touches the wings stop lifting and the glider creates more weight drag on the towplane, which if still well above the runway will be slowed and may stall. * This seems counterintuitive to me. *When the wings stop lifting, the induced drag goes away, so the drag on the towplane should decrease. *The only added drag is friction in the glider's main gear. *What am I missing here? Jim Beckman * It seems backwards to me, too, but I have asked tow pilots about this, and I was told that they feel the drag decrease when the glider comes off the ground on the takeoff roll. * I guess those wheels have a lot of drag. * * * * Alan Behind less powerful tow planes, I generally note a 3-5 knot jump in airspeed immediately following glider lift off. Frank Whiteley Brake pucks and shoes are always in light contact with the disks or drums to eliminate 'lost motion' so as to provide immediate braking action. Although small, this friction is not negligible. Aircraft tires are made from natural rubber which has very good wet and dry traction but also has higher rolling resistance than synthetic rubber. A single glider tire is also loaded heavily - sometimes beyond the load rating limit which increases rolling resistance still further. It's reasonable to expect these taken together would result in noticeable rolling resistance. On a slightly different tack, I've had badly worn drum brakes lock up on touchdown all on their own without input from me. Normally, this is not a problem and serves as a reminder to service the brakes. If the brake locked and/or a tire blew while landing on tow, the results might be 'interesting'. |
#32
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Double Release Failure
bildan wrote:
On Sep 10, 8:27 am, Frank Whiteley wrote: On Sep 10, 2:37 am, (Alan) wrote: In article Jim Beckman writes: At 14:13 08 September 2009, FBCompton wrote: Important Timing Aspect: The glider (in low tow) must not touch down much before the towplane -- this can be a hazardous aspect -- touching down well before the towplane and stalling it. The glider wings are still carrying the weight of the glider while it is flying. Once the glider touches the wings stop lifting and the glider creates more weight drag on the towplane, which if still well above the runway will be slowed and may stall. This seems counterintuitive to me. When the wings stop lifting, the induced drag goes away, so the drag on the towplane should decrease. The only added drag is friction in the glider's main gear. What am I missing here? Jim Beckman It seems backwards to me, too, but I have asked tow pilots about this, and I was told that they feel the drag decrease when the glider comes off the ground on the takeoff roll. I guess those wheels have a lot of drag. Alan Behind less powerful tow planes, I generally note a 3-5 knot jump in airspeed immediately following glider lift off. Frank Whiteley Brake pucks and shoes are always in light contact with the disks or drums to eliminate 'lost motion' so as to provide immediate braking action. Although small, this friction is not negligible. Aircraft tires are made from natural rubber which has very good wet and dry traction but also has higher rolling resistance than synthetic rubber. A single glider tire is also loaded heavily - sometimes beyond the load rating limit which increases rolling resistance still further. It's reasonable to expect these taken together would result in noticeable rolling resistance. On a slightly different tack, I've had badly worn drum brakes lock up on touchdown all on their own without input from me. Normally, this is not a problem and serves as a reminder to service the brakes. If the brake locked and/or a tire blew while landing on tow, the results might be 'interesting'. Very interesting - the white stripe on the runway costs about $100/m... (Pictures available) Tost Lilliput 4" rim failed radially around the pressed in liner as I touched down in my Std Cirrus. Air pressure forced the two parts apart against the frame. Instant locked wheel. The tar ate a hole right through the Tost 4.00x4 that I could fit a thumb through. Certainly the only time the Lilliput ever stopped 66 fast though - can't have gone much more than 50" ground roll. Have adjusted the replacement rim to give the normal useless level of braking force. Bruce |
#33
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Double Release Failure
On Sep 9, 9:27*am, JS wrote:
Sounds like it's time for a Landings On Tow Soar-O-Rama on El Mirage dry lake! Jim Yeehaa! Confidence building, fun and entertaining, useful for XC tows. I'm up for the LOT Soar-O-Rama (followed of course by awesome dry lake food, campfire, and telling of lies), but probably not at El Mirage. Last time I was there, the lakebed was being patrolled by 6 Big Land Mothers in large SUV's. Not the same atmosphere as it was in the 60's and 70's. How about Roach? |
#34
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Double Release Failure
At 19:58 10 September 2009, Uncle Fuzzy wrote:
On Sep 9, 9:27=A0am, JS wrote: Sounds like it's time for a Landings On Tow Soar-O-Rama on El Mirage dry lake! Jim Yeehaa! Confidence building, fun and entertaining, useful for XC tows. I'm up for the LOT Soar-O-Rama (followed of course by awesome dry lake food, campfire, and telling of lies), but probably not at El Mirage. Last time I was there, the lakebed was being patrolled by 6 Big Land Mothers in large SUV's. Not the same atmosphere as it was in the 60's and 70's. How about Roach? OK so what is a Big Land Mother? Jon |
#35
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Double Release Failure
On Sep 10, 2:45*pm, Jonathon May wrote:
At 19:58 10 September 2009, Uncle Fuzzy wrote: On Sep 9, 9:27=A0am, JS *wrote: Sounds like it's time for a Landings On Tow Soar-O-Rama on El Mirage dry lake! Jim Yeehaa! *Confidence building, fun and entertaining, useful for XC tows. *I'm up for the LOT Soar-O-Rama (followed of course by awesome dry lake food, campfire, and telling of lies), but probably not at El Mirage. *Last time I was there, the lakebed was being patrolled by 6 Big Land Mothers in large SUV's. Not the same atmosphere as it was in the 60's and 70's. *How about Roach? OK *so what is a Big Land Mother? Jon BLM - Bureau of Land Management. It's not as bad as I had thought, but it is a "Fee" area now, and I wouldn't go there to do the things I did when I was a teenager (a very long time ago!) http://www.blm.gov/ca/st/en/fo/barstow/mirage.html |
#36
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Double Release Failure
On Mon, 7 Sep 2009 20:46:08 -0700 (PDT), drbdanieli
wrote: ... text deleted ... Bottom line, it's not as scary as it sounds but I would suggest proper training before trying this on your own. Is anyone teaching this anymore? Barry I don't know about today, but AC Williams and his instructors at Southwest Soaring outside Dallas, TX would frequently do the landing behind the towplace with his Grob 103's during flight reviews. I did a few during BFRs in the late 80's and 90's. Mostly a non-event. The only difficult part I found was coordinating the ground deceleration so as to avoid overrunning the towrope on the rollout. Bob |
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